The present invention relates to thin film delay lines and, in particular, to resistive, thin film circuit devices defined by symmetrical patterns containing conductive pathways of non-uniform width and spacing between adjacent conductors.
Varieties of thin film devices have been constructed for high frequency circuits. Most have been directed to microwave applications. Some devices, such as discrete delay line assemblies, have been constructed for higher frequency applications.
Delay lines are frequently used to adjust timing inconsistencies at complex circuitry mounted to complex printed circuit boards that operate at ever increasing higher frequencies. Desirably therefore any delay line should accommodate these higher frequency applications by exhibiting a constant impedance over the operating delay period. Secondarily, it is desirable that the devices can be produced at reduced sizes. Examples of some discrete, multi-layer, delay line devices constructed on ceramic substrates are shown at U.S. Pat. No. 5,030,931; 5,365,203; and 5,499,442.
The subject invention provides patterned thin film devices wherein the inductive and capacitive characteristics of the conductors that define the device are tailored by varying the line width and line spacing between adjacent conductors over the device. Several delay line circuits having a nominal 50 ohm impedance characteristic are disclosed wherein non-uniformities are formed in regions of the conductors that are not bordered on both sides by adjoining conductors, that is at the input or outermost and output or innermost conductors of a spiral patterned delay line. A reduced inductance of narrowed conductors is particularly offset with narrowed line spacing to reduce the capacitance and whereby the operating Z0 of the delay lines is improved. Several alternative coil or spiral arrangements that exhibit different delays are disclosed that are constructed on rigid and flexible dielectric substrates. Necessary terminations are connected with solder filled vias and/or edge connections to the rigid or flexible substrate.
It is a primary object of the present invention to provide thin film devices having conductors of non-uniform line width and spacing between adjacent conductors to control the inductive and capacitive characteristics of the device.
It is a further object of the invention to provide thin film devices constructed from symmetrical conductor patterns, such as zigzag, serpentine, spiral or coil shapes, wherein regions of the conductors are formed with non-uniform line width and spacing between adjacent conductors to control the inductive-capacitive characteristics of the device.
It is a further object of the invention to provide alternative delay line circuits constructed from one or more coil shaped paths wherein the innermost and/or outermost conductors exhibit reduced or wider line widths and/or narrowed line spacing from other adjoining conductors.
It is a further object of the invention to provide a device with conductors of tailored shape and a ground plane of tailored thickness.
Various of the foregoing objects, advantages and distinctions of the invention can be found in alternative thin film delay line devices and circuits constructed on rigid and flexible/foldable ceramic substrates. Several coil shaped delay lines having a nominal 50 ohm impedance characteristic are defined by conductors of varying the line width and line spacing between adjacent conductors over the device. The conductor nonuniformities are formed in regions of the conductors that are not bordered on both sides by adjoining conductors.
Still other objects, advantages and distinctions of the invention will become more apparent from the following description with respect to the appended drawings. To the extent alternative constructions, improvements or modifications have been considered they are described as appropriate. The description should not be literally construed in limitation of the invention. Rather, the scope of the invention should be broadly interpreted within the scope of the further appended claims.